I am not here to defend the retcon, again.
But Luffy's fruit has shown "multiple transformations" as no other, and I claim this quit firlmy, NO OTHER fruit has shown.
It is not just a "regular paramecia".
A regular paramecia is the Noro Noro or Buggy's.
Luffy can:
- Increase in size and exponentially increase his strength (opposite of rubber)
- Pump his blood to go faster because his blood vesselse are.. Rubbery? It makes sense, he can hold higher pressure
- Make himself harder with haki, rigid yet stretchy? (Opposite of rubber again)
- Create fire (Not haki)
Even Doffy's fruit can be remotely explained with his strings, he can manipulate them to make what he wants and so on.
But Doffy's strings cannot do anything a string cannot do.
Luffy's rubber has always done whatever Luffy wanted.